Surface markers and functional characteristics of human blood lymphocytes residing in the operational "null" subset.

After removal of nylon wool-adherent B and E rosetting T cells from the human blood lymphocyte population, a small fraction remains, often denoted as "null" subset. This fraction contains lymphocytes which are highly efficient in antibody-dependent and non-selective lymphocyte cytotoxicity. These cells possess markers. About half of them carry Fc receptors, and the majority has low avidity E and C3 receptors. Removal of low avidity E receptor-carrying cells did not abolish cytotoxicity to K-562 cells. The majority of cells carry receptors for Epstein-Barr virus but cannot be infected. The cells in mixed lymphocyte culture have a low reactivity. They aare stimulated by PHA and ConA to a similar extent and differ from the cells which readily sediment as E rosettes: these respond stronger to PHA. The "null" fraction may contain stem cells common for both T and B lineages.